Magnetic tapes can be used for information storage. Typically, writing, reading and erasing information from a magnetic tape involves manipulating the magnetization of particles contained on the tape such as, for example, by directly contacting the magnetic tape with a tape head. Generally, the tape head applies a magnetic field to the magnetic tape during writing and erasing, and the magnetic tape induces a current in the tape head during reading.
Disks can be used for information storage. Certain disks contain a material that changes crystalline state upon exposure to heat. Generally, writing information on and erasing information from such a disk involves exposing portions of the disk to an energy beam, such as a light beam. The energy interacts with the disk and is converted to heat, forming portions of the disk where the material has changed from a crystalline state to an amorphous state, or vice-versa. Usually, reading information from such a disk involves irradiating the disk with a low energy beam and measuring one or more properties of the reflected energy beam.